The present invention relates to a programming method for a robot, a programming apparatus for a robot, and a robot control system.
In arc welding, it is necessary to teach to a robot so that the tip of a tool referred to as a torch and a junction portion may strictly agree. In addition, the posture of the torch is also important in order to maintain task quality. Accordingly, if the junction portion has a complicated shape, it takes a lot of time to provide teaching for the junction portion. Therefore, a teaching-free approach has been developed to reduce the number of teaching processes. However, there is no arc welding robot available that has realized complete teaching-free task, leaving some teaching tasks necessary to be performed by human beings.
Japanese Laid-Open Patent Publication No. 8-123536 discloses a welding torch posture teaching method. In the method disclosed in the present document, a reference plane is calculated from a taught torch position, to obtain a posture with respect to the reference plane by using input values of a target angle and an advance/retraction angle, thereby acquiring a desired welding torch posture. Further, in the present method, for each torch position, each posture in which desired target angle and advance/retraction angle are reflected is created and written in a program that inputs the torch positions. In such a manner, the present method calculates a reference plane based on a torch position input beforehand, and therefore can automatically calculate a welding torch posture if an operator inputs angle data of desired target angle and advance/retraction angle in a reference plane. Therefore, in teaching a welding torch posture, manual tasks for causing a robot to assume a desired posture are unnecessary, thereby simplifying the teaching tasks.
Japanese Patent No. 3200106 discloses a method for recognizing a preset shape of a workpiece with a laser sensor to obtain the position of a groove and then correcting a position of the torch tip and a torch posture. In the method disclosed in the present document, reference taught data is created roughly beforehand. Then, at the time of execution of welding, to modify the reference taught data, a groove shape is imaged with a laser sensor or the like mounted on a robot. That is, the taught data is corrected based on a result of the imaging by the laser sensor, so that it is only necessary to create rough taught data beforehand, thereby simplifying the teaching tasks.
Japanese Laid-Open Patent Publication No. 9-76065 discloses a welding torch robot that realizes a desired torch position/posture by copying a welding seam with a laser sensor in real time during welding. In the method disclosed in the present document, taught data created beforehand is corrected based on image data obtained using the laser sensor. Accordingly, welding can be continued even if a three-dimensional displacement occurs in a workpiece. The present invention does not aim at simplification of teaching tasks. However, it suggests a possibility for simplification of teaching tasks in creating rough taught data and correcting taught data in real time so as to provide a desired welding position/posture by using a sensor when welding.
According to Japanese Laid-Open Patent Publication No. 8-123536, a reference plane is determined based on a position of the tool such as a torch, so that it is necessary to program the position with strict accuracy. When programming the position, it is necessary to move a robot to a desired position manually. Accordingly, if there are a lot of points to teach, a lot of labor is required for teaching tasks. Moreover, by the present method, even with a slight difference in workpiece shape, a task is required to modify or add the positions of the tool.
The inventions disclosed in Japanese Patent No. 3200106 and Japanese Laid-Open Patent Publication H9-76065 aim at correcting displacements of a workpiece. The displacement is caused by an error in machining or setting of the workpiece. However, recently, the workpiece machining errors have been eliminated and, further, a workpiece fixing jig is improved so that no displacements may occur. Therefore, no displacements would occur on at least 90 percent of the workpieces to be machined.
Accordingly, in an environment free of workpiece displacements, it is of no use to use a position detection sensor such as the laser sensor or mount the position detection sensor on a welding robot during welding by use of the welding robot.
On the other hand, in the case of simplifying teaching tasks by using a position detection sensor such as a laser sensor in the environment free of workpiece displacements, the following problems occur.
(1) When executing taught data, that is, each time actual tasks are performed using a tool, detection tasks are performed by the position detection sensor. This has a large effect on the cycle time.
(2) One laser sensor is necessary for each robot. This increases introduction costs.
(3) Also when actual tasks are performed using a tool, it is necessary to mount the position detection sensor. This increases power consumption.